Summary At about 1700 Pacific daylight time, near the head of Knight Inlet, British Columbia, the VIH Helicopters Ltd. Bell 206B Jet Ranger helicopter (registration C-GWUF, serial number1182), with only the pilot on board, touched down in a toe-in landing at an unprepared helicopter landing site in a steep, stream gorge. After the pilot had stabilized the helicopter with the toes of the skids in contact with the surface, one of the two waiting passengers entered the left front seat. The pilot then motioned the second passenger to enter the helicopter in the left rear seat. As this passenger transferred his weight from the ground to the helicopter skid, the helicopter slipped backwards on the loose rock surface, and the pilot applied collective pitch and forward cyclic in an attempt to maintain the hover attitude. The pilot was unable to prevent the helicopter from turning quickly left, and he lost visual reference and control. The helicopter became airborne, struck trees adjacent to the landing site, rolled over, and came to rest on its left-hand side, almost inverted. Both passengers sustained minor injuries and the pilot sustained serious injuries. The helicopter was substantially damaged; there was no post-impact fire. The accident site is located at 5104'24"N latitude and 12532'37"W longitude, at an elevation of about 1350feet. Ce rapport est galement disponible en franais. Other Factual Information History of the Flight Earlier that day, after flying the two forest-harvesting engineers on a reconnaissance of the area, searching for potential pick-up sites, the helicopter pilot landed them at a drop-point on the ocean shoreline below the accident site. The engineers were evaluating the area for possible logging as they climbed up the steep gorge, eventually stopping at the site they had assessed as being suitable for helicopter pick-up. They then called the pilot to pick them up. The helicopter was parked at the base camp about two nautical miles (nm) away. The pilot took off for their location and searched for them while remaining in radio contact. Once the pilot located the passengers and the pick-up site, he assessed the site as suitable and flew to the touchdown zone they had prepared. The pilot had not previously landed at the landing site (see AppendixA). The slope of the selected site required the pilot to conduct a toe-in landing using the hover-exit procedure. He lowered the helicopter in the hover, placed the toes of both skids on the surface, and stabilized the helicopter in that configuration. When the pilot indicated it was safe to do so, the first passenger climbed onto the left skid, opened the left front door, entered the cockpit, and strapped into the left seat using the full seat restraint. The helicopter remained in a stable toe-in position. The pilot then motioned the second passenger to enter the helicopter. The passenger climbed onto the left skid and began to move aft; however, as he transferred his full weight onto the skid, the toes of the skids abruptly slipped downslope. The pilot instinctively applied collective lever, forward cyclic and right pedal to counter the sudden movement, but at this time, the pilot was unable to see out through the windshields because of increasing condensation on the inside surfaces and the rain and mist on the outside. He lost all visual reference with the terrain. The helicopter became airborne, with the second passenger now clinging to the left skid. Almost immediately, the passenger released his grip and dropped to the (surface) ground. The helicopter, now turning and rolling to the right, struck trees with the rotor blades and crashed onto the rock ledge about 10feet ahead of the pick-up point. After the helicopter came to rest, the engine continued to run. Even though there was some smoke initially in the cabin, no fire erupted. The passenger in the left seat turned off the fuel valve and closed the throttle to shut down the engine. The two passengers then removed the pilot from the wreckage, administered appropriate first aid to the pilot and themselves, and set up a camp to await rescue. Both passengers were trained first-aid attendants and were skilled in survival in the forest. Through a combination of satellite telephones and hand-held radios, the passengers communicated with several agencies to advise them of their accident, and they remained in good communication throughout the evening. One of the passengers retrieved the emergency locator transmitter (ELT) from the wreckage and activated it manually. Search and Rescue Following the occurrence, at about 1700Pacific daylight time,1 the passengers established communication with the base camp and the operator to advise them of the accident. Canadian Department of National Defence Search and Rescue was promptly alerted and rescue efforts were set in place within 30minutes of the accident. Tasked by the Joint Rescue Coordination Centre in Victoria, British Columbia, search and rescue (SAR) aircraft from 19Wing Comox flew to the area to search for the survivors. Their efforts were hampered by nightfall and poor weather conditions. Toward midnight, a break in the fog cover enabled rescuers in a Cormorant helicopter to find the pilot and passengers and winch them on board. They were transported to hospital at Comox, British Columbia. Landing Area The landing site was a terraced ledge, about 40feet wide, in a steep gorge on the west face of the mountain, and adjacent to a rapidly flowing waterfall. The site was surrounded by tall trees and almost-vertical rock faces, and the landing surface consisted mainly of loose rock and forest debris, constantly wet from the waterfall flow. The distance from the touchdown point to the waterfall rock face was about 50feet, and the helicopter ended up about 20feet away from the waterfall (see Photo1). Photo 1. View of touchdown area The landing site is located at 1350feet above sea level. The temperature was not formally recorded at the site, but was in the order of 5C. Given such values, the density altitude would have been about 300feet. Weather The weather at the time of the accident was reportedly not conducive to sustained visual flight because it was raining heavily and there was widespread, layered fog in the whole mountainside area. Nonetheless, the specific flight path chosen by the pilot was navigable with visual reference to the ground, and the landing site was discernable. The winds were shifting in strength and direction, at speeds estimated up to 15knots. In general, the prevailing winds at the accident site would have been erratic at that time of the evening, and there was a possibility of downflowing air. The weather conditions on the following day were reported by site personnel as quite similar to the day of the accident, and Photo2 shows the weather conditions likely faced by the accident pilot. Photo 2. View through windshield of likely weather conditions Pilot The pilot was certified and qualified for the flight in accordance with existing regulations. He held a valid Canadian commercial pilot licence - helicopter and had accumulated about 1450total flying hours, of which 350hours were on Bell206 helicopters. He had worked for VIH Helicopters Ltd. as a line pilot for about six months and met all company recurrent ground and flight-training requirements. Both his initial and recent flight training in mountain operations with VIH Helicopters Ltd. had been extensive, and he knew of the conditions that characterize unprepared landing sites in mountainous regions. The pilot was appropriately rested before commencing duty on the day of the accident. The Knight Inlet operation had started on 23October2006, two days before the accident, and the pilot had flown about four hours for the project. He was characterized by clients and peers as being a competent and cautious pilot. Helicopter Information The accident helicopter is a Bell206B-II Jet Ranger, manufactured in 1973 by the Bell Helicopter Company in Texas, United States, as serial number 1182. The investigation team was unable to gain access to the accident site because of the inhospitable terrain, and the wreckage was initially examined from the air to the degree possible. Later, the helicopter was removed from the ledge by a professional salvage team, and subsequently examined by investigators in a secured facility at Campbell River, British Columbia. There was no indication of any pre-accident anomaly or malfunction with the flight controls, the drive train, or any other system that could have contributed to the accident circumstances. The maintenance logs and records indicated that the helicopter was certified, equipped, and maintained in accordance with existing Canadian regulations and approved procedures. Engine Information The engine installed in the accident helicopter was a Rolls Royce (formerly Allison) gas turbine 250-C20 model engine, serial number CAE-820707, which is rated at 400shaft horsepower (shp). Engine maintenance logs record that the engine was maintained in accordance with existing Canadian regulations and approved procedures. In consideration of the reported sequence of events, the investigation ruled out both engine mechanical malfunction and loss of performance. The engine manufacturer's development of the 250-C20 series engine has led to a more powerful and reliable model, the 250-C20B, developing 420shp, which in helicopter applications, provides greater power available to the main rotor gearbox. Allison/Rolls Royce has implemented an engine upgrade program that converts the 250-C20 to the higher-performance C20B model. Incorporation of the following items forms the largest part of the conversion process (reference: Allison Commercial Engine Bulletin CEB-1053 17November1975 with revisions): C20B compressor and turbine modules; modified engine accessory gearbox; modified engine fuel control system; new associated engine data plates; and improved cockpit engine monitoring gauges. The C20 engine compressor and turbine modules are no longer available from the manufacturer, and C20B modules are being used as airworthy replacements during C20engine repair and overhaul. According to Rolls Royce, such replacement is an approved practice. The incorporation of the C20B modules alone does not upgrade the C20 engine, and although engine efficiency and performance is increased with the C20Bcomponents, the engine must continue to be operated at the original certificated specification limits. Such was the case with the Rolls Royce 250-C20 installed in C-GWUF, as only the compressor and turbine sections were C20B components. Bell206B Type Certificate The Bell 206B-II helicopter was originally type-certificated in the United States with the Allison (now Rolls Royce) 250-C20 model turbine engine only. The upgraded Bell206B-III helicopter uses the higher-performance Rolls Royce 250-C20B engine. By design, the main rotor transmission in both these helicopters is limited to a maximum of 317shp from the engine, and consequently the engines are de-rated to meet this limitation. The type certificate for all versions of the Bell206 helicopter is now held in Canada by Bell Helicopter Textron Canada Limited of Mirabel, Quebec. Because the 250-C20B model engine is not on the approved type certificate for the Bell206B-II, it cannot be installed in that helicopter. Nonetheless, replacement 250-C20 engines with the C20B modules are being installed in this model helicopter as an approved practice. Although the engine continues to be operated at C20 limits, the increased engine performance essentially permits maximum performance for the Bell206B-II at higher-density altitudes. Consequently, even though the theoretical specification power difference between the two engine models is 20shp, in practical terms, given this hybrid C20 engine, the available power differential would be significantly less. Cabin Heating System in C-GWUF The cabin heating system in the accident helicopter was installed as approved supplemental type certificate (STC) SH3887NM by Air Comm Corporation of Boulder, Colorado, United States, dated 24December1987 with revisions. This installation forms part of the Bell206 Transport Canada-approved rotorcraft flight manual (RFM) as flight manual supplement (FMS) 206H-200, which applies to Bell206A and 206B model helicopters only. The heater is a bleed-air type that uses bleed air from the engine compressor section and mixes it with cabin air to provide heat for the occupants and for the windshield defrosting vents. In C-GWUF, the original defog blower fan could also be used to circulate heated air through the defroster vents. No operational restrictions exist when the heater is installed in a Bell206 with a Rolls Royce 250-C20B engine. However, the 250-C20 engine has limitations because the original STC program only validated the C20B engine. According to the normal operating procedures in the Air Comm Corporation heater FMS, the heater and defroster control is to be selected off before take-off, and during hover, descent, and landing. The supplement also warns that Flight with heater and defroster operating is prohibited during take-off, hover and landing for aircraft equipped with the C-20 engine. Accordingly, for the case of the C20 engine only, the heater and defroster must be selected off during take-off, hover, and landing. For the C20B engine, the performance degradation with the heater on is relatively small, and by way of example, for flight conditions similar to the day of the accident, there would have been no noticeable effect on either engine power or hover performance. The effect on the C20 engine has not been quantified directly, but since the maximum specification power output is only 20shp less than the C20B model, it is likely that the performance effect is similarly slight. Nonetheless, the limitation does exist, and the accident pilot complied with the operating instructions in the approved RFM. In the final stage of the approach to the landing site, the pilot turned the heater and defroster off and kept the defog vent blower fan running. There is no Canadian requirement for a heater to be fitted to a helicopter. Although Canadian Aviation Regulations (CARs) are silent on the requirement for a heater in an aircraft, they do prescribe that the windshield be able to be demisted. In the Canadian weather environment, a heater is necessary for effective windshield demisting/defogging. Helicopter Weight and Balance Shortly before take-off on the accident flight, the pilot filled the fuel tank with Jet A-1 fuel to a fuel quantity gauge indication of about 50USgallons. This amount equates to about 340pounds of fuel, which was more than adequate for the proposed mission. The helicopter flew for about 10minutes before the accident. TSB investigators calculated that the gross weight of the helicopter at the time of the accident was no more than 2550 pounds (one passenger aboard); had the helicopter taken off with the second passenger on board, the weight would have been in the order of 2700pounds. With reference to the Bell206B helicopter RFM, the maximum gross take-off weight is 3350pounds (internal load).2 The calculations also indicated that both the longitudinal and lateral centres of gravity (CG) were within certified limits.3 The lateral CG, however, moved close to its left limit when the second passenger transferred his weight onto the left skid; the lateral CG quickly returned to the centre when that passenger dropped off the skid. Hover Performance The hover-out-of-ground-effect (HOGE) hover ceiling chart in the Bell206B RFM provides maximum allowable gross weight for varying conditions of pressure altitude and outside air temperature to ensure that the helicopter can hover without the performance benefit of ground effect. For the conditions at the time of the accident, the HOGE chart showed that the weight of the helicopter with the three occupants on board would have been well within the out-of-ground-effect performance capability of the helicopter (see AppendixB). Hover Exit (Toe-in Landing) Procedure Toe-in landings are normally used where the slope of the landing area exceeds the prescribed off-level landing limits of the helicopter. The toe-in landing procedure permits the drop-off or pick-up of passengers or cargo by the pilot touching the helicopter down on just the forward portion (the toes) of the skids. Passenger and cargo movement then takes place while the helicopter is balanced on the toes. This requires the pilot to set a high collective position to maintain a significant amount of powerwithin about 15percent of hover powerto prevent the helicopter from rotating tail-down about the ground contact point (the toes). The toe-in landing and passenger pick-up or drop-off procedures are finely balanced manoeuvres, requiring the pilot to smoothly and constantly adjust collective pitch and cyclic stick position as each passenger boards or disembarks the helicopter. The practice of the toe-in pick-up is not without risk, but when carried out in a controlled and cautious manner, the procedure is practical and is an accepted technique throughout the helicopter industry. During toe-in landings, there is the potential of significant longitudinal and lateral CG shift during passenger and cargo operations. For this reason, all movements are cautious and slow to allow the pilot to progressively feel the helicopter's response to the changing loads. In the event of a sudden weight change, however, the helicopter's response may be rapid and greater than the pilot had anticipated, thus leading to larger fuselage movements and subsequently larger flight control movements (that is, pilot inputs) to counter those movements. It is also possible that the pilot could lose visual and tactile contact with the surface and unintentionally become airborne. Section 4, Annex B (Hover Exit Operations), of the Transport Canada-approved VIHHelicopters Ltd. company operations manual identifies the risks of entering or leaving a helicopter in hover flight and provides instruction and procedures for pilots to carry out these operations. A review of the specific operational practices carried out at Knight Inlet revealed no deviation from these instructions. Crashworthiness/Survivability The injuries to the passenger in the left front seat and the pilot were caused by impact forces when the helicopter rolled over and struck the terrain. The passenger outside the helicopter received minor injuries when he dropped from the skid before the helicopter crashed. Medical information and injury patterns indicate that the pilot and passenger in the cockpit were wearing full seat restraints, and the pilot was wearing a flight helmet (see Photo3). Both these factors contributed to their survival of the impact and the lessening of their injuries. Photo 3. Damage to pilot's helmet Loss of Visual Reference It is a known characteristic that the interior surfaces of plexiglass in a Bell206 cabin, particularly the windshields, are susceptible to fogging in high-humidity conditions, thus degrading a pilot's ability to see clearly. To counter this problem, a defog vent blower fan is installed in the cockpit and, coupled with the aircraft heater, provides a recirculating airflow to reduce the fogging of the windshield and side windows. There is no opportunity for the pilot to manually wipe the surfaces to clear the moisture away from the windshield in the hover since the pilot needs both hands to safely manoeuvre the helicopter. An additional restriction to vision for a Bell206 pilot occurs in rain because the helicopter is not equipped with windshield wipers. When the helicopter is in forward flight, rain on the windshield runs off with a small amount of beading. However, at low forward speeds, and particularly in the hover, the airflow over the windshield is reduced and water can accumulate and cause significant restriction to visibility. Photo4 shows the forward visibility from a Bell206 cockpit at low forward speed in moderate rain. Photo 4. Forward visibility in moderate rain It is also a frequent event that, when a person in wet clothing with rain enters the cockpit, the windshields quickly fog up, even with the vent blower operating. Normally, this is a temporary condition and the condensation is quickly reduced or removed. However, there are circumstances when the humidity is so high that the fogging does not dissipate sufficiently and the pilot experiences a prolonged period of marginal visibility through the windshield. Visual Illusion One of the phenomena that leads to visual illusions in hovering flight occurs when the surface of a body of water ripples or moves, as a result of rotor downwash for example, giving the helicopter pilot a strong perception that the helicopter is moving even though it is actually stationary. A similar effect can be seen with rapidly falling water, such as a waterfall, where the pilot is influenced by the rapid water movement and can lose hover reference. Additionally, beaded water droplets moving across the windshields can introduce a sensation of movement. Yet, another phenomenon in hovering flight happens when the main rotor blades pass through saturated air causing downwash condensation trails that may, in an already reduced visibility situation, lead to a visual illusion of motion. Furthermore, in certain lighting conditions, the curvature of the windshield is conducive to reflection of shiny or bright objects in the cockpit, and such reflections can interfere with a pilot's depth perception, particularly with rain and condensation on the windshields. Pre-flight Safety Briefings In accordance with both VIH Helicopters Ltd. and the contracting company's policies, on the morning of Monday, 23October2006, the pilot and the lead engineer conducted thorough safety briefings for all personnel involved in the Knight Inlet operation before the job began. The briefings were comprehensive and comprised review and discussion of all appropriate operational procedures, such as toe-in landings, boarding techniques, and protocols for emergency procedures and communication.